Extra slow firing schedule for heavy pots

[mark_m]

I'm firing an L&L kiln with an LT3140 controller. Am not acclimated to these digital controllers and am firing a somewhat precious load with pieces up to 1/2" thick walls and some going to 1" on the feet. I want a very conservative schedule to be on the safe side. Have had problems in the past with the default slow bisque schedule.  Here is what I'm thinking:

180 rate 50 hold 8 hrs

210 rate 15 hold 1

213 rate 1.5 hold 1

650 rate 150

700 rate 50

1050 rate 150

1100 rate 80

1655 rate 150

Cone 06 rate 80 hold 1

This will be my first programmed schedule - part of me still wishes I just had knobs to turn but I know this will be so much more convenient when I'm used to it... Thanks for any thoughts!

-Mark M

[neilestrick]

I don't think you're going to get any benefit in climbing super slow from 180 to 213. You're also putting too much faith in the ability of a controller to do super slow climbs. You might get regular temperature differences of 15 degrees during any climb. I wouldn't mess with rates less than 50 degrees per hour. Slower than that you're just wasting time. Better to get to the temp and hold. I would just do a long preheat at 180F, then climb at 75/hour all the way up. It will take about 24 hours after the preheat, but better safe than sorry.

[mark_m]

Thanks Neil. I am running a program kind of integrating your feedback with my schedule, i.e. still slowing down a bit more for chemically combined water and quartz inversion. Thanks very much for your thoughts!

[CactusPots]

Mark, your work sounds a lot like mine.  I have texture sprig attachments, added feet, joinery and  lots of (paper) slip work.   Some pieces as big as 25lbs wet.   What I have found most effective is a substantial time under plastic to equalize the moisture before drying.  Then it dries  under bath towels.  The final step is a couple of days in the sun.  Using that, this is my bisque schedule.

40 degrees per hour to 120

hold 1 hour

80 degrees per hour to 200

hold 1 hour

250 degrees per hour to 1000

no hold

300 degree per hour to 1823 (cone 06)

It's 5 hours from start to closing the lid (propped open about 3" for burn out)

Very close to 10 hours complete.  I don't have breakage with this routine unless I miss guess how long a piece is in any phase.  It seems to me this is the best compromise between too slow and too fast.

 

 

[mark_m]

On 11/17/2019 at 8:06 AM, CactusPots said:

Mark, your work sounds a lot like mine.  I have texture sprig attachments, added feet, joinery and  lots of (paper) slip work.   Some pieces as big as 25lbs wet.   What I have found most effective is a substantial time under plastic to equalize the moisture before drying.  Then it dries  under bath towels.  The final step is a couple of days in the sun.  Using that, this is my bisque schedule.

40 degrees per hour to 120

hold 1 hour

80 degrees per hour to 200

hold 1 hour

250 degrees per hour to 1000

no hold

300 degree per hour to 1823 (cone 06)

It's 5 hours from start to closing the lid (propped open about 3" for burn out)

Very close to 10 hours complete.  I don't have breakage with this routine unless I miss guess how long a piece is in any phase.  It seems to me this is the best compromise between too slow and too fast.

 

 

Thanks - I got through that last firing ok, will compare  your schedule to what I ended up with!

[CactusPots]

If I'm really nervous about a piece I'll run the first part of the schedule, to 200 degrees, shut it off closed and then run the schedule as normal.  I think you could run that on a pretty green and big piece and get away with it if you needed it for a load.

[CactusPots]

On 11/17/2019 at 8:06 AM, CactusPots said:

Mark, your work sounds a lot like mine.  I have texture sprig attachments, added feet, joinery and  lots of (paper) slip work.   Some pieces as big as 25lbs wet.   What I have found most effective is a substantial time under plastic to equalize the moisture before drying.  Then it dries  under bath towels.  The final step is a couple of days in the sun.  Using that, this is my bisque schedule.

40 degrees per hour to 120  3 hours

hold 1 hour

80 degrees per hour to 200 120-200 1hour

hold 1 hour

250 degrees per hour to 1000  200-1000 3.2 hours

no hold

300 degree per hour to 1823 (cone 06) 1000-1823 2.74 hours

It's 5 hours from start to closing the lid (propped open about 3" for burn out)

Very close to 10 hours complete.  I don't have breakage with this routine unless I miss guess how long a piece is in any phase.  It seems to me this is the best compromise between too slow and too fast.

 

 

But now that I'm trying larger pots, I'm seeing what I'm told are quartz inversion cracks and now I realize, I'm doing 300 an hour through QI.  Also, that the overall firing is too slow and I'm wasting time (money) at the lower temps.  There are 3 or 4 cracks running up the side wall of this wide low planter.

Also, this pot is almost the full width of the 23" electric kiln shelf, I'm making a deal on a reconditioned 1227 Skutt.  I'm told the larger kiln will be kinder to bigger pots like this.

Here's something I don't understand.  If I add up the times on the schedule I have listed, it comes to 12 hours.  The actual firing time is very consistent at 9.5 hours.  What am I missing?

 

[liambesaw]

Because your first ramp isn't real.  You aren't starting from 0 degrees.  The first ramp is more like 1 hour

 

[oldlady]

hi guys,  i do not make huge pots but i do fire green to glaze in a single firing.   my normal load is very heavy, sometimes 9 shelves with spacing between 1 1/2 inch and 3 1/2 inches with flat slab pots.   i do make sure everything is dry, sometimes if in a hurry i will dry them in my kitchen oven at 180 degrees.   the point is, my normal firing time is 14 hours or a little more.  for years.  using the slow glaze with a preheat of 1 hour.